Air delivery systems for building ventilation may consist of several centrifugal fans operating in parallel, perhaps in an array (e.g., a bank or assembly) in order to act together to provide more airflow than one alone could provide to a common area, space or shared discharge plenum. At times, a fan in that array becomes inoperative due to mechanical failure, electrical supply issues, or planned system functions (as but a few examples) while other fans in that array continue to operate. When one of the fans is not operating (i.e., is inoperative), it may be important to prevent the reverse flow of air (backflow) through the inoperative fan. Backflow may occur when the pressure downstream of the fans acts to force air back through (in a reverse direction) the inoperative fan(s). This is, of course, undesired, as it may reduce pressure downstream of the fan (e.g., such that it is less than an intended, design pressure), among possibly having other negative impacts. Embodiments of the inventive technology may help to resolve such negative impact(s) by obstructing such backflow through an inoperative fan of a fan array while allowing (and not unacceptably impacting) “forward” flow when that fan is operating, in addition to having other applications. Note that the inventive technology may even have application to a centrifugal fan that is not in an array, but that may be susceptible to undesired backflow when that fan is inoperative if its flowpath is not obstructed at that time.
The inoperative fan backflow problem has been known for some time and there are conventional approaches to its solution. But the use of conventional dampers, for example, placed at the inlet to the fans has the disadvantage of reducing fan performance during normal operation and increasing the noise of the fan due to flow disturbances created by the damper. Certain conventional approaches may also be either mechanically complex (e.g., by requiring centrifugally actuated linkages and springs to, e.g., move a damper from one configuration to another) or require external attachment at the fan inlet (or external actuating assemblies), both of which can reduce fan performance, lead to imbalance problems during fan rotation, and/or increase noise. Embodiments of the inventive technology seek to alleviate one or more of these problems.